1,4-Butanediol is an important raw material in the chemical industrial field. It is used in the preparation of highly valuable products, such as: polybutylene terephthalate (PBT), polyurethane (PU), tetrahydrofuran (THF), and .gamma.-butyrolactone. Traditionally, 1,4-butanediol is prepared from acetylene and formaldehyde by the Reppe process. However, as acetylene has limited availability and has recently become expensive, processes for preparing 1,4-butanediol from other resources besides acetylene are gaining importance.
Among various processes for making 1,4-butanediol from other than acetylene, a process in which allyl alcohol is used as a starting material has the best potential for development. The process comprises the steps of subjecting allyl alcohol to a hydroformylation reaction in the presence of carbon monoxide and hydrogen to generate an intermediate 4-hydroxy-butanal, followed by a hydrogenation step to produce 1,4-butanediol. The reaction scheme is as follows. ##STR1##
The study of the process of allyl alcohol hydroformylation was first reported by H. Adkins and G. Kresek [J. Amer. Chem. Soc., 78,388 (1948), and ibid., 79,3051 (1949)], wherein tetracarbonyl hydrido cobalt was used as a hydroformylation catalyst. However, it had a low reactivity and thus the reaction required a high temperature and a high pressure to proceed. Furthermore, both the yield and selectivity of 4-hydroxy-butanal were very low in that system. Later, C. K. Brown and G. Wilkinson [Tetrahedron Letters, 22,1725 (1969) and J. Chem. Soc. (A) 2753 (1970)] and B. Fell and M. Barl [Chemiker Zeitung, 101,343 (1977)] followed H. Adkins and G. Kresek's method, except that hydrido carbonyl tris(triphenyl phosphine) rhodium and tertiary phosphine ligands were used as catalysts to increase the reaction rate by 100 to 1000 times, and as a result the yield and selectivity were greatly improved. The above method proposed by Brown et al. seemed to be commercially more practical.
However, allyl alcohol is still not a chemical substance that is available on a bulk commercial scale. Thus, in order to produce 1,4-butanediol from allyl alcohol commercially, a steady supply of allyl alcohol, at a low cost, is necessary. Currently, the following three typical methods are commonly used for the preparation of allyl alcohol: ##STR2##
However, allyl alcohol produced with the above methods is still too costly for use in making 1,4-butanediol on an industrial scale. Recently, a process for preparing allyl alcohol at a higher yield and at a lower cost has been developed. As such, processes for preparing 1,4-butanediol from allyl alcohol have become more competitive. The referred to process for preparing allyl alcohol comprises the steps of subjecting a mixture of propylene, acetic acid, and oxygen to acetoxylation to produce allyl acetate and water, and hydrolyzing the allyl acetate to produce allyl alcohol the chemical reactions are shown in the following schemes:
CH.sub.2 .dbd.CHCH.sub.3 +CH.sub.3 COOH+1/2O.sub.2 .fwdarw.CH.sub.2 .dbd.CHCH.sub.2 OCOCH.sub.3 +H.sub.2 O PA1 CH.sub.2 .dbd.CHCH.sub.2 OCOCH.sub.3 +H.sub.2 O.fwdarw.CH.sub.2 .dbd.CHCH.sub.2 OH+CH.sub.3 COOH
The allyl alcohol prepared from the above process is in an azeotropic mixture which contains about 30% H.sub.2 O and a small amount of allyl acetate. As a result, it is therefore difficult to separate allyl alcohol from the mixture. Moreover, purification of allyl alcohol from the mixture increases the cost of producing 1,4-butanediol when pure allyl alcohol is needed as a starting material.
There are several inventions in the field. Kuraray company in Japanese Patent Publication Sho 51-29412 (1976) disclosed a process for preparing 1,4-butanediol from pure allyl alcohol which comprises the steps of subjecting pure allyl alcohol, carbon monoxide, and hydrogen to a hydroformylation reaction in a solvent containing a catalyst of rhodium carbonyl complex; extracting the reaction mixture with water; separating the solution into an organic phase containing catalyst and an aqueous phase containing aldehyde; recovering the organic phase and recycling it back to the hydroformylation system; and reacting the aqueous phase with hydrogen to produce 1,4-butanediol.
The distinctive feature of the process of Sho 51-29412 is in the process of extracting the hydroformylation product with water and separating the catalysts from the reaction mixture after hydroformylation. This process avoids the formation of high-boiling-point compounds from aldehydes during distillation processes for separating hydroformylation products currently used in the chemical industry (J. Falbe ed., "New Syntheses with carbon monoxide", Springer Venlya, 1980, p.171-). The accumulation of such high-boiling-point compounds in the reaction system would otherwise deteriorate the activities of the catalysts. Furthermore, the high temperature in the distillation process itself can also deactivate the catalyst. Thus, the process of Sho 51-29412 disclosed by Kuraray company prevents the above discussed disadvantages of the distillation.
Although the Kuraray process has advantages, it is only applicable to systems in which pure allyl alcohol is used as a feed stock.
As earlier mentioned it is costly to use purified allyl alcohol made from allyl acetate. On the other hand, if the mixture of allyl acetate, water and allyl alcohol is used as a feed stock in hydroformylation, the catalyst can suffer from deactivation (see Japanese Patent Kokai Sho 50-30809, and Japanese Patent Publication Sho 57-25018). Thus, Kuraray further proposed an improved process for preparing 1,4-butanediol from allyl alcohol containing allyl acetate as the starting material, which process was disclosed in Japanese Patent Publication Sho. 57-25018.
The process of Sho 57-25018 comprises extracting the hydroformylation product with water; contacting a portion of the hydroformylation catalyst solution with an alkaline aqueous solution; and recycling the catalyst solution through the hydroformylation system. In Sho 57-25018, it was indicated that the activity of the catalyst was stabilized, but after a thorough study by the inventors of the present Application, it has been found that the process of Sho 57-25018 may have solved some of the old problems encountered in the art but still left other problems to be solved (details will be discussed hereinafter). Further, it has been found that the process proposed by Sho 57-25018 was not the most desirable.
After intensive investigation by the inventors of the present invention, it has been found that the deactivation of the catalyst in the hydroformylation of allyl alcohol feed stock that contains allyl acetate and water can be attributed to the presence of an acid compound. The process disclosed in Japanese Patent Publication Sho 57-25018 solved the problem of hydroformylation catalyst deactivation. However, that process requires two extraction operations after the hydroformylation. In the first extraction by water, the aqueous phase contains an acid compound which causes a contamination and a generation of high-boiling-point materials in the successive hydrogenation reaction process. In the second extraction with alkaline aqueous solution a waste water is generated. Thus, the process needs further improvement.